As is well known and understood, a wide variety of problems come into play in operating a radio-communications system in a hostile environment. For example, message traffic flow from user to user and from node to node or from relay station to relay station is usually controlled by centralized units which are of far higher complexity, value, weight and bulk than the relay or user station. In digital communications systems this centralized unit frequently is a computer which operates together with a large collection of peripheral equipment. This means that the whole system is hierarchically organized such that the operational availability of the whole system depends on the availability of the highest member in the hierarchy, the central control unit. Someone who is interested in deactivating the system only has to concentrate his efforts on deactivating the central control unit. His task is simplified by the fact that these units are much easier to detect and easier to destroy than the lower and more expendable members of the hierarchy.
Also contributing to problems in their usage, such communications systems most often operate at UHF frequencies, where tall antenna structures are required for line-of-sight transmissions--especially in wooded areas and in localities where other obstructions such as buildings predominate. High antenna structures increase system vulnerability to detection, electrical interference and physical destruction.
With the technology frequently employed in their construction, and with the manners of their implementation, such communications systems offer further disadvantages in that their component parts have to be repaired, replaced and maintained--because of their expensive costs and non-disposability. This leads to additional problems by requiring a dedicated supply, storage and repair organization whose own limits in availability contribute to limits in system survivability.
In order to make a communications system less detectable one has to obscure its appearance. While nothing can be done to reduce a given physical size, one can try to hide system units, e.g., in natural or man-made cover and one can give its electrical emissions a noise-like appearance, e.g., by spreading its electrical emissions over a large frequency range by so-called spread-spectrum methods. However, physical hiding interferes with line-of-sight operation and spectrum spreading increases the cost, complexity and, hence, the physical bulk of the system units.
In order to make communications and communications systems less vulnerable one usually tries to supply a sufficient number of back-up copies of system units and messages, i.e., one increases redundancy. This again can only be bought at higher costs and complexity or one has to accept a decrease in system performance by only partly utilizing the system, i.e., by slowing down or reducing the message traffic.
Other disadvantages of such prior art communications systems will also be readily recognized: (a) The high cost involved because of limited production runs; (b) The continuing use of increasingly obsolete designs so as not to incur the additional costs of new developments; (c) The high degree of training required in the utilization of the communication equipments; (d) The difficulty in transporting about, because of weight, size and bulk.